Assorted LVS troubles

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: Assorted LVS troubles
From: Tobias Klausmann <klausman@xxxxxxxxxxxxxxx>
Date: Thu, 23 Feb 2006 10:47:15 +0100

I have two questions regarding LVS trouble that bit me recently.

I'm using vanilla 2.4.31 with not patches on PIV hardware,
balancing around 2-3k Connection/s in peak. Management software
is keepalived, method is Direct Routing, I don't do automagic

1) It seems like Linux does not ARP as often as I expect it to. I
thought no matter how much communication happens between two
hosts, there usually is an ARP request (who-has) every five
minutes. But in the case of keepalived, which checks the
Realservers, I see no ARP requests at all, just normal
communication. If I flush the arp cache for an IP, there's one
ARP request (and reply), then no more. Does normal TCP
communication "refresh" the ARP table entries? There are no
hardcoded ARP entries in my setup.

The logical network setup is like this:

[[RSs]] <-------- [LB] <-------- [client]
   |      VLAN A          VLAN B    ^
   |                                |

I see no ARP requests on VLAN A. I.e. the OS on LB learns the MAC
address of the RSs once, then keeps that knowledge forever.

I realize that this *probably* isn't an IPVS problem in and of
itself, but haven't seen it anywhere else.

2) When I last tested IPVS on 2.6, I sometimes saw "stuck"
connections. The LB had connections in its counters (and probably
in the IPVS conntrack table, too) that expired ages ago. Even
days or weeks after the last packet for such a farm was sent to
the LB, they were still there. Sometimes, even deleting the
entire farm and adding it again didn't help. While the farm is in
use, the number of those connections steadily increases. Is this
problem known (and/or fixed)?


You don't need eyes to see, you need vision.

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